In the paints, coatings, inks, and adhesives (“coatings”) industries, it is desirable to produce low viscosity dispersions of resins that include pigments and/or particulate fillers that exhibit excellent dispersion of the pigment and filler particles in which (i) the pigments and fillers, particularly sub-micron sized or nano-sized, pigments or fillers are de-agglomerated and reduced to their primary particle size; (ii) the subject particles are physically separated from each other or uniformly spaced in the polymer; (iii) the resultant dispersions comprising polymeric resins, pigments, and fillers, and/or combinations of pigments and fillers are stable; and (iv) the pigments and fillers do not settles or re-agglomerate. Nano-sized pigments and nano-particles can be dispersed and reduced to their primary particle size in a low viscosity format. It is further desirable that the low viscosity dispersions as described above maximize the weight percent loading of the pigments and/or fillers while minimizing the weight percent loadings of the polymer, liquid solids so that a final polymeric paint, coating, or ink composition can be produced in and of itself having very low viscosity, high tinting strength caused by optimized pigment concentrations and/or maximized mechanical properties caused by homogenous dispersion of maximized concentrations of fillers. The polymeric resin solids used as the mill base for the dispersions can be 100% liquid solids or a combination of liquid solids and solvents. There is a further, particular need in the referenced industries to have very low viscosity dispersions as described above that either have very low solvent contents or, preferably, no solvent content that can be used for producing, for example, low viscosity, 100% solvent free, radiation curable coatings. A complete description of the nature and benefits radiation curable coatings can be found in the publication entitled “Radiation Curing of Coating.” Joseph V. Koleske, ASTM International, 100 Barr Harbor Drive, West Conoshohocken, Pa., 2002.
Every day, throughout the world, manufacturing companies of all sizes use paints, coatings, and inks to protect and decorate a wide variety of composite or laminate products ranging from heavy equipment parts, automobile parts, appliance casings, metal cans, and other metal sheets that are pre-painted and then shaped into finished metal containers and panels. Traditionally, solvents have been used in high concentrations to produce low viscosity paints and coatings that have high pigment and filler loadings and that can be easily and smoothly applied to plastic, wood, and metal substrates with such coatings having optimized aesthetics, opaque pigment color, and optimized mechanical and chemical resistance properties. Whereas traditional solvent-base coatings have solvent contents from 40% to 90% by total coating weight, there is a growing demand and need by industry to dramatically reduce or eliminate the use of solvents in coatings due to environmental and safety concerns. High solids coatings and radiation curable coatings are considered to be ecologically friendly and contain little or no solvents. These coatings are also far more energy efficient due to reduced energy costs for curing and other economic efficiencies, such as accelerated curing times. There is a need for low viscosity, high filled pigment and/or filler dispersions in polymeric resins that are highly stable and homogenous that can be used to produce commercially viable, low viscosity paints, coatings, and ink compositions that are (i) low in solvent concentration or solvent free, (ii) have excellent application characteristics such as flow and leveling equal to their solvent-based counterparts; (ii) and are equally as functional in aesthetic and physical quality as high solvent coatings.
Dispersions are often quite expensive and it is highly desirable to have a low viscosity dispersion having a high concentration of pigments and/or particulate fillers so that optimized amounts of dispersion are used in the final coating compositions. Low viscosity, highly filled dispersions can be used to make very thin coating films, having excellent opaque colors. Very thin films, applied to substrates, use coatings more efficiently, lowering coating costs, lowering curing energy costs, while increasing productivity. On the other hand, low viscosity, highly filled dispersions can be used to make thick coating compositions for casting such as casting prototypes. In any case, low viscosity, highly filled dispersions are advantageous when optimizing finished coating viscosities, color fastness, and mechanical properties.
The publication, Hyperdispersants, Technology & Benefits, The Lubrizol Corporation, HD-002, July, 2008, teaches that polymeric hyperdispersants produce improved pigment dispersions by attaching polymer chains to an anchoring group such as a pigment which separates or de-agglomerates the pigment particles and sterically stabilizes the dispersion of particles. The publication further teaches that the hyperdispersant or polymeric chain competes with the dispersion resin and other additives for attachment to pigment or particle surfaces. Therefore, it is taught to use only a hyperdispersant such as Solsperse® to attach to either a surface treated or an un-surface treated pigment or particle in a dispersion of liquid resin and pigments particles. Any other additives should be added after the pigment dispersion is let down and mixed into the final coating formulas so that other dispersing and surfactant additives do not detach the hyperdispersant (anchoring polymer chain) from the pigment particle surface. The publication goes on to teach that pigment particle surfaces should, preferably, not be treated since the hyperdispersant will not attach to a treated surface. It also teaches that it is preferred to use a high viscosity resin because a low viscosity resin wets the pigment surface and also competes with the hyperdispersant for attachment to the pigment surface, and, as such, better results can be attained by using a higher viscosity resin. When applied as directed, the pigment dispersion containing a hyperdispersant, liquid resin, a pigment, and solvents will have a lower viscosity than a similar pigment dispersion without a hyperdispersant. The publication fails to teach the use of a hyperdispersant in combination with other polymeric dispersants or chemicals, and, in fact, teaches not to use a hyperdispersant with any other dispersant or chemical when making pigment particle dispersions because the pigments will re-agglomerate and the pigment dispersion will be unstable. Dispersions made from hyperdispersants alone are limiting in producing a low viscosity dispersion with high concentrations of pigments and/or particles.
U.S. Pat. No. 6,660,374 B2 discloses radiation curable compositions that comprise solid, amorphous glass particles that are transparent to radiation, such as UV light, that improve the radiation curing behavior of such coatings. The patent teaches that such glass particles can be de-agglomerated and more fully dispersed by silane surface treating the glass particles prior to dispersing the glass particles into the coating. However, the patent does not disclose or teach the use of dispersants added to a resin to make a pre-dispersion of either pigments and/or glass particles.
POSS® Titania, Hybrid Plastics, February, 2007 discloses the use of POSS (Polyhedral Oligomeric Silsesquioxane) silanols to coat the surfaces of silicas and metal oxides, such as TiO2, in order to enhance dispersion and make a dispersion more stable. The publication also teaches that the POSS silanols are used alone to treat pigment surfaces such as TiO2. The publication does not teach or disclose the use of POSS silanols with hyperdispersants. Dispersions made from POSS alone are limiting in producing a low viscosity dispersion with high concentrations of pigments and/or particles.